Investigation of recrystallization and grain growth of copper and gold bonding wires
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CENTLY, copper bonding wire has attracted attention as an alternative to gold bonding wire. Copper has better electrical conductivity than gold, and it is cheaper to produce. However, fabrication of copper wire still needs more research on drawing and annealing processes in order to optimize the quality of the bonding wire. Axisymmetrically drawn products of face-centered-cubic (fcc) metals with medium and high stacking fault energies have typical textures consisting of double fibers with a majority ,111. component and a minority ,100..[1–8] It is known that the ,100. fiber becomes dominant after recrystallization but changes back to the ,111. component upon further annealing at higher temperatures. This texture transition has been reported in copper wire.[8] In the early stage of the annealing process, the ,100. component is prevalent due to recrystallization. In the later stage, the ,111. or ,112. component becomes dominant because of abnormal grain growth. These investigations are based on both X-ray diffraction and electron backscatter diffraction (EBSD) measurement. Recrystallization and grain growth of gold bonding wires were previously investigated using EBSD.[9] The ,100. component grows into the ,111. fiber during recrystallization. In addition, the ,100. and ,111. fibers consume other texture components. As coarsening takes place, the average grain size of both ,100. and ,111. oriented grains increases. Grain boundaries with high misorientation angles between the ,100. and ,111. orientations tend to migrate into the ,111., and the overall texture shows a higher volume fraction of the ,100. component after JAE-HYUNG CHO and K.H. OH, MSEs, are with Seoul National University, Seoul, South Korea 151-742. Contact e-mail: [email protected] A.D. ROLLETT, MSE, is with Carnegie Mellon University, Pittsburgh, PA 15213. J.-S. CHO, Y.-J. PARK, and J.-T. MOON, MKE Research Lab, are with MK Electron, Pogok-Myeon, Yongin-Si, Kyunggi-Do, South Korea 151-742. Manuscript submitted February 12, 2006. METALLURGICAL AND MATERIALS TRANSACTIONS A
recrystallization. This is explained by an energy advantage for the ,100. fiber. During plastic deformation, gradients in the plastic strain give rise to geometrically necessary dislocations (GNDs) in order to maintain lattice continuity.[10,11,12] The energy stored through cold work must include a fraction stored as GNDs. Small lattice rotations due to GNDs can be measured and characterized using local orientation measurements with EBSD.[13] Thus, the internally stored energy in a material can be at least partially measured via intragrain misorientation angles, for example, with grain average misorientation (GAM) or scalar orientation spread (SOS). The SOS or GAM of the ,100. component was measured to be lower than that of the ,111. in gold wires.[9] This difference in stored energies provides driving force for the ,100. component to grow into the ,111. or other orientation components. In the beginning of annealing, subgrain growth (or the migration of low-angle grain boundaries (LAGBs)) oc
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